This invention relates generally to clothes washing machines and more particularly to a washing machine having an improved suspension system.
As is known in the art, under certain operating conditions, washing machines may vibrate and in aggravated cases may even move (or "walk") across a floor. This undesirable vibration occurs generally when the horizontal forces exerted on the washer's supporting feet exceed the resistive frictional forces between the supporting feet and the floor. Such a condition may be referred to generally as causing "frictional" mode vibration. Note that the frictional forces between the supporting feet and the floor are a function of the vertical loads exerted on the supporting feet and the coefficient of friction associated with such feet.
One way known in the art for reducing the tendency of the washing machine toward frictional vibration and walking is to increase the frictional forces between the floor and the supporting feet, generally by improving or increasing the frictional forces between the floor and the supporting feet. This can be achieved by increasing the coefficient of friction associated with the supporting feet. More particularly, the coefficient of friction may be increased by using various materials, such as rubber, on the bottom of the supporting feet to contact the floor. However, higher coefficient of friction materials are now employed on current washers and frictional walking persists.
Another way known in the art for increasing the frictional forces between the floor and the supporting feet is to increase the vertical loads on the washer's supporting feet. High vertical loads can be achieved by large washer weights and an even distribution of weight on each of the supporting feet. However, as lighter weight washers are less expensive to manufacture, increasing vertical loads by increasing washer weight may not be a suitable solution.
Various schemes for improving the evenness of the load distribution on the washer's supporting feet have been attempted. For example, vertically adjustable supporting feet are commonly used. With this arrangement, the height of such feet are adjusted when the washer is installed by adjusting the screw fastened supporting feet. After the height adjustments are made, the supporting feet are secured in place to prevent vertical movement thereof during washer operation. However, accurate installation is extremely difficult and time consuming. When installing the washer on a compliant floor, all supporting feet may be in contact with the floor but not equally loaded (i.e. carrying one-quarter of the washer weight). Without elaborate instrumentation, it is generally not possible to accurately measure the loads on the supporting feet. Moreover, as the horizontal forces necessary to overcome the reduced frictional resistance of the lighter loaded supporting feet and the floor are relatively small, frictional mode walking may result.
Another way to increase the evenness of the load distribution on the supporting feet is to use what has been referred to as "self-leveling" feet. This arrangement includes a horizontally extending member interconnecting a pair of the supporting feet with such member having horizontally extending tabs inserted into slots in the sides of the washing machine base. This arrangement is intended to allow the height of the pair of interconnected feet to be adjusted in accordance with the floor surface. However, the interconnected feet are designed to lock into place and thus, if the spring rate of the floor surface changes, frictional walking may result. Moreover, as the spring rate of a floor generally changes due to humidity and/or structural settling, the loads on the washer feet may not remain even. Thus, with this arrangement, the performance of the washer may degrade after installation.